In centerless grinding art it is common knowledge that to achieve "rounding up" of the workpiece, the axes of the workpiece, grinding wheel, and regulating wheel must not lie in a common plane; i.e., the grinding wheel and the regulating wheel must not contact points on the workpiece which are 180.degree. apart.
The principal reason for this is the fact that if a lobe was present on the workpiece diameter, the workpiece would be thrown toward the grinding wheel when the lobe contacted the regulating wheel; thus, out-of-roundness would be perpetuated.
Most centerless grinders are constructed so that the grinding wheelhead does not move, and is affixed to the base of the machine. The regulating wheelhead is generally attached to a slide housing which may be slid on ways upon the base, toward or away from the grinding wheel. These ways are most generally parallel to some reference on the base, such as the floor line, (however, they may be slid along any other plane which is fixed relative to the base).
The commonly used method of taking the workpiece out of the line of action between the centers of the regulating wheel in the grinding wheel, is generally to elevate the workpiece diameter above the line of centers of the wheels of the machine. Elevation of the part is usually accomplished by means of a workrest blade which supports the workpiece for its entire length during any grinding process, and further supports work which is retracted from the grinding position durin infeed grinding.
Infeed grinding is performed very simply when the workrest blade is attached to the regulating wheel slide housing in a fixed position relative to the regulating wheel. In this manner, when the regulating wheel is retracted from the grinding wheel, a finished workpiece is removed from the workrest blade and a rough workpiece is placed in the crotch formed by the workrest blade and regulating wheel, thereafter to be ground when blade and wheel are advanced toward the grinding wheel. In infeed grinding the axes of rotation of the grinding wheel and regulating wheel lie in a common plane so that only rotary motion is imparted to the workpiece.
In thrufeed grinding, however, it is necessary to provide a component of force to propel a rotating workpiece along an axial path, beginning at the point of entry of the workpiece between the regulating wheel and grinding wheel, and continuing until the finished workpiece then exits from the opposite side of the two wheels at which time the grinding process is complete. This necessary component of force to propel the workpiece along its axial path is derived from the regulating wheel.
The regulating wheel imparts a tangential force to the surface of the workpiece when in its normal position (wheel axis parallel to workpiece axis) therefore, when the regulating wheelhead is swiveled in the vertical plane, vertical and horizontal components of force result from the now-tilted tangential force of the regulating wheel.
However, it is apparent from the "skewed cylinder" effect, that the regulating wheel, when pivoted in a vertical plane, will then only have a point contact with the workpiece and thus be limited to the driving influence it can exert on the workpiece. To establish contact along the entire length of the workpiece then the regulating wheel is dressed with a wheel truing device in such a manner as to dish out the regulating wheel in an axially-curved shape, to create a "wraparound" contact line along the axis of the workpiece to effect regulation of the workpiece travel.
When it becomes necessary to insert a larger or smaller diameter workpiece, the contact line is no longer valid even though the same center height may be maintained. The axis of the regulating wheel may be swiveled to re-establish this contact line. However, this workpiece will no longer be parallel to either the vertical plane of the blade or the axis of the grinding wheel. It then becomes necessary, through dressing the regulating wheel, to alter the difference between the front and rear diameter of the wheel, to re-establish this parallelism. This correction is necessary because the work axis and the swivel axis do not lie in the same plane. This redressing of the regulating wheel consumes an appreciable amount of time, and decreases useful life of the wheel.
It is, therefore, an object of the present invention to obivate and overcome the difficulties involved in the prior art thrufeed device.
Another object of the present invention is to provide a means whereby thrufeed grinding setup may be achieved with minimal time.
A further object of the present invention is to increase life of regulating wheels.
A still further object of this invention is to centralize axial "wraparound" of the regulating wheel with respect to a horizontal plane through the work.